## Why Do We Live in Three Dimensions?

by Amy Shira Teitel[/caption]

Day to day life has made us all comfortable with 3 dimensions; we constantly interact with objects that have height, width, and depth. But why our universe has three spatial dimensions has been a problem for physicists, especially since the 3-dimensional universe isn’t easily explained within superstring theory or Big Bang cosmology. Recently, three researchers have come up with an explanation.

Most astronomers subscribe to Big Bang cosmology, the model that proposes that the universe was born from the explosion of an infinitely tiny point. The theory is supported by observations of the cosmic microwave background and the abundance of certain naturally occurring elements. But Big Bang cosmology is at odds with Einstein’s theory of general relativity – general relativity doesn’t allow for any situation in which the whole universe is one tiny point, which means this theory alone can’t explain the origin of the universe.

The incompatibility between general relativity and Big Bang cosmology has stumped cosmologists. But almost 40 years ago, superstring theory arose as a possible unifying theory of everything.

Superstring theory suggests that the four fundamental interactions among elementary particles – electromagnetic force, weak interaction, strong interaction, and gravity – are represented as various oscillation modes of very tiny strings. Because gravity is one of the fundamental forces, superstring theory includes an explanation of general relativity. The problem is, superstring theory predicts that there are 10 dimensions – 9 spatial and one temporal. How does this work with our 3 dimensional universe?

Superstring theory has remained little more than a theory for years. Investigations have been restricted to discussing models and scenarios since performing the actual calculations have been incredibly difficult. As such, superstring theory’s validity and usefulness have remained unclear.

But a group of three researchers, associate professor at KEK Jun Nishimura, associate professor at Shizuoka University Asato Tsuchiya, and project researcher at Osaka University Sang-Woo Kim, has succeeded in generating a model of the universe’s birth based on superstring theory.

Using a supercomputer, they found that at the moment of the Big Bang, the universe had 10 dimensions – 9 spatial and 1 temporal – but only 3 of these spatial dimensions expanded.

The team developed a method for calculating matrices that represent the interactions of strings. They used these matrices to calculate how 9 dimensional space changes over time. As they moved further back in time, they found that space is extended in 9 directions, but at one point only 3 directions start to expand rapidly.

In short, the 3 dimensional space that we live in can result from the 9 original spatial dimensions string theory predicts.

This result is only part of the solution to the space-time dimensionality puzzle, but it strongly supports the validity of superstring theory. It’s possible, though, that this new method of analyzing superstring theory with supercomputers will lead to its application towards solving other cosmological questions.

So would that mean that at the point of origin of the universe one would find the other 6 dimensions?

I recall a previous comment discussion where the lack of granularity effects on light observed from distant sources seemed to be a problem for extra dimensions?

Not discerning an obvious yes or no from all that

The answer, if there is an answer in this business, is that this dispersion is not a necessary aspect of all these theories. This data constrains theories, where a good number of them are eliminated.

LC

I guess it’s way to early for an obvious yes or no. A definite maybe — that may be possible.

In other words everywhere in the Universe.

I’ve found two of their papers:

Expanding (3+1)-dimensional universe from a Lorentzian matrix model for superstring theory in (9+1)-dimensions;

Expanding universe as a classical solution in the Lorentzian matrix model for nonperturbative superstring theory.

But only in the lay-man use of the term “theory”. String theory is not a valid theory in the scientific sense. Until now it is still and only a mathematical toy (as far as I know) and has not produced any measurable results making possible its falsification.

I think that even this described result cannot be “observed”. But if I’m wrong, please correct me.

Knots can only exist in 3-dimensions. They are essential to life, at least as we know it (proteins). So, we can only exist in a 3-dimensional universe and, I suspect, can only observe the universe we exist in.

The KEK mathematicians have only shown that a string model is consistent with one aspect of our 3-D universe. If we can’t observe anything else, it’s math not science.

So I guess these 6 rather small dimensions might explain why the observable 3D universe is rather uniform across vast 3D distances? Every point in “our” 3D universe must be closely connected somehow, or how else would you explain the similarity of everything everywhere? (Perhaps some kind of “inertia” in laws of nature and physical constants, but wouldn’t that also call for an extra dimension where that inertia “lives”??)

Well just a layman musing here, I hope someone will take the bait and expand/explain this weird similarity phenomenom a bit further..

Perhaps Fred Hoyle has had the last laugh as “Big Bang” was originally a disparaging term for the idea he hated, by causing so many people’s misconceptions of it. Perhaps cosmologists should run a competition to find a new more correct name for the creation event, perhaps with an apt acronym as a bonus.

The steady state cosmology model of Hoyle, Bondi, Gold and Narlikar is dead as a doornail. If completely fails to match observational data. Further, if the universe were steady state something curious would happen. The smallest perturbation would cause it to either expand or collapse. This perturbation could be a quantum fluctuation.

LC

It is amazing to contemplate, all the complexity that rises from “nothing”.

If you watch the Science Channel you need only one caveat. Be skeptical of anything Michio Kaku says.

If you Google any of those topics, you will have enough reading material to last a lifetime. Enjoy

What I wonder is this… If, at some point, 3 dimensions expanded enough to be what we sense today… Might it be possible, since expansion is still continuing, that the universe reaches a point where another dimension starts to expand… What would be the effect? Would we even be able to preceive it? How would that change the “laws” of physics?

It should be obvious, if the focus was more on physics than mathematics, that gravitation is not a force. Gravitation is a distortion of spacetime geometry in the presence of mass. The only time gravitation and force coincide is when gravitation is interrupted, as at or below the surface of a large mass surrounding a geometric vortex.